dict-ws bnd fails build when 'test' folder is missing

Issue

• Git will not add folders that are empty.
• bnd.bnd refuses to build if the test folder is missing (https://gitlab.stud.idi.ntnu.no/TDT4250/examples/tree/master/dict-ws/tdt4250.dict1.servlet)

Fix

Add an empty file, like test/.gitkeep, so the folders are kept in git.